Regular use of aspirin may reduce the incidence of colorectal cancer (CRC). However, it is unclear through which mechanism aspirin exerts its effect, in whom it decreases CRC risk and in whom it causes side effects. Recently, the imbalanced gut microbiome was linked to inflammation and CRC risk. The main hypothesis for this study is that aspirin may decrease CRC risk via targeting the gut microbiome. The study will be a randomized placebo-controlled double-blinded design, recruiting 50 healthy subjects, 50-75 years old, from the PRospective Evaluation of SEPTin 9 (PRESEPT) cohort living in the greater Twin Cities area, who will receive either aspirin or placebo for 6 weeks.